Systems and methods for determining shooter locations with weak muzzle detection

• US 20070237030A1
• Filed: 08/23/2005
• Published: 10/11/2007
• Est. Priority Date: 08/23/2005
• Status: Active Grant

• Current Assignee: Raytheon BBN Technologies Corp. (Rtx Corporation)
• Original Assignee: BBNT Solutions LLC (Rtx Corporation)
• Inventors: Mullen, Richard, Barger, James, Milligan, Stephen, Brinn, Marshall
• Granted Patent: US 7,359,285 B2
• Time in Patent Office: Days
• US Class Current: 367/127
• CPC Class Codes: G01S 5/22 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/28 takes precedence
• CPC Class Codes: Y10S 367/906 Airborne shock-wave detection

Abstract

Systems and methods for locating the shooter of supersonic projectiles are described. The system uses at least five, preferably seven, spaced acoustic sensors. Sensor signals are detected for shockwaves and muzzle blast, wherein muzzle blast detection can be either incomplete coming from less than 4 sensor channels, or inconclusive due to lack of signal strength. Shooter range can be determined by an iterative computation and/or a genetic algorithm by minimizing a cost function that includes timing information from both shockwave and muzzle signal channels. Disambiguation is significantly improved over shockwave-only measurements.

Claims

1. A method for estimating a shooter range by detecting shock wave and muzzle blast, comprising:

measuring shockwave-only signals at a plurality of spaced acoustic sensors forming an antenna;

measuring a muzzle blast signal at the plurality of acoustic sensors;

determining from the measured shock wave and muzzle blast signals an initial estimate of the shooter range;

assuming an initial bullet velocity and a bullet drag coefficient; and

iteratively computing an instantaneous bullet velocity along a bullet trajectory to obtain an updated shooter range.

2. The method of claim 1, wherein iteratively computing comprises performing a predetermined number of iterations.

3. The method of claim 1, wherein determining the initial shooter range includes computing a time-difference-of-arrival (TDOA) between the shockwave-only signals and the muzzle blast signals, and an arrival angle.

4. The method of claim 1, wherein iteratively computing comprises defining a convergence criterion and accepting the updated shooter range as a final shooter range if a relationship between successively determined updated shooter ranges satisfies the convergence criterion.

5. The method of claim 4, wherein the relationship between successively determined updated shooter ranges is a difference between the successively determined updated shooter ranges.

6. The method of claim 4, wherein the relationship between successively determined updated shooter ranges is a percentage change between the successively determined updated shooter ranges.

7. The method of claim 1, wherein the computed bullet velocity is set to the speed of sound if the computed bullet velocity is less than the speed of sound.

8. The method of claim 1, wherein the updated shooter range is considered invalid if a bullet trajectory angle and an arrival angle are greater than a predetermined value.

9. The method of claim 8, further including, if the updated shooter range is invalid, applying a genetic algorithm (GA) by:

defining an initial population of the GA, the population having a predetermined number of individuals, each individual represented by a 3-tupel which includes an assumed shooter range, a missed azimuth (MA) and a missed elevation (ME) of the bullet trajectory;

performing the GA for a predefined number of generations;

computing residuals for the individuals in each generation; and

selecting in each generation the solution having the smallest residual as the individual which survives unmutated.

10. The method of claim 9, and further including the step of selecting, after the predefined number of generations have been performed, the solution having the smallest residual as the updated shooter range.

11. The method of claim 9, further comprising

for each 3-tupel in a generation, performing a predetermined number of iterations to compute a revised shooter range, wherein the residuals for the individuals in each generation are computed with the revised shooter range.

12. The method of claim 9, wherein applying the GA comprises applying crossover and mutation operators to the population in a generation.

13. The method of claim 12, wherein applying the crossover operator includes exchanging at least one of missed azimuth and missed elevation between two individuals from the population in a generation.

14. The method of claim 12, wherein the mutation operator comprises field-mutation, incremental mutation, and no mutation.

15. The method of claim 14, wherein the field-mutation operator replaces a value of the 3-tupel with a randomly selected value.

16. The method of claim 14, wherein the incremental mutation operator induces a small mutation in all fields of the 3-tupel.

17. The method of claim 14, wherein the no-mutation operator leaves the individuals in a generation unaltered.

18. A method for disambiguating a projectile trajectory from shockwave signals and a limited number of muzzle blast signals, comprising:

measuring shockwave-only signals at five or more spaced acoustic sensors forming an antenna;

measuring muzzle blast signals on at most four of the sensors;

determining from the shockwave signals Time-Differences-Of-Arrival (TDOA) information for sensor pairs;

performing for a predefined number of generations a genetic algorithm with an initial population that includes a predetermined number of individuals, each individual represented by a 4-tupel which includes shooter azimuth, shooter elevation, missed azimuth and missed elevation;

computing residuals for the individuals in each generation, said residuals including a least-square fit of a combination of TDOA shockwave and muzzle blast signals; and

if a ratio of the solution having the smallest residual and its ambiguous alternate solution is greater than a predefined value, designating the solution having the smallest computed residual as the disambiguated projectile trajectory.

19. A method for extracting a signal from a muzzle wave in the presence of a shockwave signal, comprising:

defining a time window having a width corresponding to a time required for a muzzle wave to traverse a sensor array;

detecting the shockwave signal;

after detection of the shockwave signal, advancing the window and measuring total energy received in the window as a function of time; and

associating a maximum of the measured total energy with the muzzle signal.

20. The method of claim 19, wherein measuring the total energy includes integrating the measured energy over the window.

21. The method of claim 19, further including identifying shockwave echoes and disregarding portions in the detected signal caused by the shockwave echoes.

22. The method of claim 19, further including determining a peak signal value in the window producing the maximum total energy and identifying the peak signal value as the muzzle signal, if the peak signal value is greater than the measured total energy in the window by a predefined ratio factor.